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My touch faucet died. I can use a z44n mosfet to activate the solenoid with the 6V battery pack but I need to have the polarity switched each use to drive the solenoid in the opposite direction with the next touch. What can I put in the oval in the diagram to make the polarity switch on the battery?

enter image description here

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  • \$\begingroup\$ There is a schematic button on the editor toolbar. It has symbols for batteries, solenoids and MOSFETS. You should also be clear about the solenoid wires, how many, what resistance and whether or not the solenoid has to be kept powered to hold the valve shut and what type of switch it is. \$\endgroup\$ – Transistor Mar 13 at 14:59
  • \$\begingroup\$ If the solenoid is a spring loaded flip flop then no idle current and a suitable pair of SPDT relays for solenoids with clamp diodes is what is needed. To make what is called a full-bridge voltage doubler. Measure coil DCR and report back in question. All these assumptions. Contact arc or FET failures are most common from contact bounce. \$\endgroup\$ – Tony Stewart EE75 Mar 13 at 16:35
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What can I put in the oval in the diagram to make the polarity switch on the battery?

There is nothing effective that can be put in the oval area that will work. IRFZ44N MOSFETs (if that is what you mean) are not bi-directional. They will heavily conduct in the reverse direction due to their bulk diode.

Neither is it sensible to connect the faucet sensor directly to the gate of a MOSFET. These are electrostatic sensitive devices and can be easily destroyed without protection circuits.

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  • \$\begingroup\$ No, I mean they are not bi-directional (as stated). "not uni-directional" means bi-directional and MOSFETs are not bi-directional in operation. \$\endgroup\$ – Andy aka Mar 13 at 15:29
  • \$\begingroup\$ @AnalogKid I'm really struggling to understand what we are talking about here (I did mention the bulk diode) so, if you'd prefer, delete your comments if you are satisfied (I'll delete mine too) or be clearer about what you are asking me. I don't bite (much) LOL \$\endgroup\$ – Andy aka Mar 13 at 15:58
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You need to use an H-Bridge to reverse the load polarity. You could also use a DPDT ON-OFF-ON, but there is now way to do it with one MOSFET. The MOSFET way is far more complicated.

schematic

simulate this circuit – Schematic created using CircuitLab

schematic

simulate this circuit

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